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Optical Characteristics of Strontium Titanate Films Obtained by the Sol–Gel Method
摘要： Using data of multiangle spectrophotometry and spectral ellipsometry in the UV and visible ranges, spectra of the refractive indices and absorption coefficients and width of the forbidden band of one- and five-layer strontium titanate films obtained by the sol–gel method have been calculated. Layer-by-layer deposition of sol on quartz substrates, from one to five layers, leads to an increase in film porosity from 4 to 33%. This causes a decrease in the refractive indices in the middle part of the visible spectrum from 2.33 to 1.87, which leads to a decrease in the reflectance and an increase in the transmittance or transparency of five-layer films. With an increase in the heating temperature of such films from 500 to 750°C, a shift of the absorption band maximum from 239 to 253 nm takes place and the optical width of the forbidden band decreases from 4.63 to 4.20 eV. The absorption band maximum of the single-layer film falls on the wavelength of 252 nm, and its optical width of the forbidden band is 3.96 eV.
关键词： Strontium titanate films,optical characteristics,forbidden band width,sol–gel method,refractive indices,absorption coefficients
更新于2025-09-09 09:28:46
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The role of point defects and defect gradients in flash sintering of perovskite oxides
摘要： The present study investigates the impact of point defects and their redistribution on the flash sintering process. Strontium titanate was chosen as a model system for the group of perovskite ceramics. The characteristics of flash sintering of strontium titanate were analyzed with different acceptor dopant concentrations. The onset of flash sintering was found to be dependent on the acceptor dopant concentration, as expected by the increasing conductivity. A gradient in the microstructure was found after flash sintering with larger grain sizes at the negative electrode. TEM-EDS measurements indicated Ti enrichment at the positive electrode for undoped strontium titanate and strong acceptor segregation for doped strontium titanate. In contrast, grain boundaries at the negative electrode were found to be stoichiometric for the undoped case and the acceptor segregation was less obvious for the doped case. Based on these results and the space charge behavior of strontium titanate, we infer that a gradient of the oxygen vacancy concentration is induced by the electric field during flash sintering: at the positive electrode the oxygen vacancy concentration is higher than at the negative electrode. For strontium titanate it is well known that a high oxygen vacancy concentration reduces the space charge and, hence, acceptor segregation, which agrees well with the experimental findings. Overall, the present study highlights the importance of point defect gradients and space charge for flash sintering of strontium titanate, which may be applicable for many other functional ceramics.
关键词： Flash sintering,Space charge,Non-stoichiometry,Strontium titanate,Point defects
更新于2025-09-04 15:30:14
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Effects of doping by aluminum or lanthanum on the electrical and electroluminescence properties of Ca0.6Sr0.4TiO3:Pr thin films
摘要： Thin-film electroluminescent devices containing Ca0.6Sr0.4TiO3:Pr, Al-doped Ca0.6Sr0.4TiO3:Pr, or La-doped Ca0.6Sr0.4TiO3:Pr phosphors were prepared by a conventional sol–gel and firing method. Doping by Al improved the performance of the device markedly, in that its current-starting voltage and emission-starting voltage decreased, its luminance response became more rapid, and its relative quantum efficiency increased. Almost all the effects of doping with La were opposite to those of doping with Al. On stacking thin films of Al-doped Ca0.6Sr0.4TiO3:Pr and La-doped Ca0.6Sr0.4TiO3:Pr, the current-starting voltage and the emission-starting voltages decreased further and the relative quantum efficiency increased further in comparison with the Al-doped film. The effects of doping by Al and La can be understood by assuming that Ca0.6Sr0.4TiO3:Pr separates into n-type and p-type semiconducting regions as a result of the electromigration of oxygen vacancies, and that the oxygen-vacancy density increases or decreases on doping by Al and La, respectively.
关键词： Perovskite titanate,Praseodymium,Lanthanum,Oxide thin film,Aluminum,Electroluminescence
更新于2025-09-04 15:30:14
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A new design of the YIG/MTC joint brazed by bismuth-based glass
摘要： The paper uncovers an underlined mechanism of joining Yttrium Iron Garnet (YIG) and Magnesium Titanate Ceramic (MTC) with a bismuth-based glass braze. The proposed joint design has not been investigated until present. The central hypothesis is as follows. The brazed bismuth-based glass microstructure and the resulting mechanical strength of a YIG/MTC joint design support favorably a good bonding of the interface domains. The supporting evidence includes the following: (i) the bismuth-based glass features good wettability on YIG and MTC, (ii) the sequence of the coefficients of thermal expansions (YIG, bismuth-based glass, MTC) is in a favorable succession. The study reveals that the interface reactions form: (i) a lamellar phase and YBO3 whiskers at the YIG/Bi25 interface, (ii) both MgFe2O4, and Bi4Ti3O12 whiskers in addition to Zn2Ti3O8 reaction layer at the MTC/Bi25 interface, and (iii) Fe2O3 phase along the brazing seam. The mechanical integrity of joints has been studied as well.
关键词： Magnesium titanate ceramic,Whiskers,Microstructure,Bismuth-based glass braze,Yttrium iron garnet ferrite
更新于2025-09-04 15:30:14
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Preparation and Characterization of Ba1-xSrxTiO3 by Sol-Gel Method
摘要： Barium strontium titanate (BST) with formula (Ba1-xSrxTiO3) has been synthesized by sol-gel method with different stoichiometric compositions (x = 0.3, 0.4, 0.5, 0.6). The raw materials which used to prepare compounds are (Ba,Sr) acetate as a source (Ba,Sr) and titanate isopropoxide source. The FE-SEM images showed that the particles size reduced from 464 to 13 nm when strontium concentration increased from 0.3 to 0.6. The X-ray diffraction studies have confirmed that Ba0.7Sr0.3TiO3 sample have the tetragonal phase while remaining samples have a cubic phase. The intensity of the major peaks were decreased and shifted toward higher 2θ angles when Sr2+ ions increases.
关键词： Barium strontium titanate,Curie Temperature,Ferroelectric materials,Perovskite structure
更新于2025-09-04 15:30:14
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Structural Modification, Synthesis Mechanism and Properties Analysis of Li4Ti5O12 Anode Materials
摘要： Li4Ti5O12 microsphere was synthesized by hydrothermal method. The effects of amount of lithium hydroxide, hydrothermal time and sintering temperature on properties of sample were studied. The synthesis mechanism of Li4Ti5O12 microsphere was preliminary analyzed. The structural characterization was analyzed by X-ray diffraction, and the morphology was investigated by scanning electron microscopy and transmission electron microscopy. The properties of galvanostatic charge, discharge and cycle stability were also studied. The results indicated that when 2.55 mmol LiOH?H2O reacted with 0.2 g hydrolysate, the sample had pure phase, when the hydrothermal condition was 36 h and 180 oC, the structure of sample particle was intactly spherical. The volume average size of samples were between 400 nm to 600 nm. The charge and discharge voltage plateau of samples were very stable. When the sintering temperature was 700 oC, the first discharge capacity was 148.3 mAh?g-1 at 0.1 C. After 10th cycle, the discharge capacity retained at 132.5 mAh?g-1.
关键词： hydrothermal method,electrochemical property,hydrothermal condition,Lithium titanate
更新于2025-09-04 15:30:14
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Recent development on modification of synthesized barium titanate (BaTiO3) and polymer/BaTiO3 dielectric composites
摘要： In order to fabricate barium titanate (BaTiO3) particles with high purity, small particle size and narrow distribution of particle size, the synthesis methods and doping elements should be properly selected. Compared to polar polymers, non-polar polymers have advantages on the fabrication of miniaturized and lightweight electronic devices, due to excellent process-ability and little endogenous heat generated in the electric field. To avoid the aggregation of BaTiO3 particles in polymer matrix, several nanometer thick organic coating on the BaTiO3 surface is needed. What’s more, the alignment of BaTiO3 and hybrid use of fillers can further improve the dielectric properties of polymer/BaTiO3 composites.
关键词： Barium titanate,Synthesis methods,Dielectric properties,Surface modification,Polymer composites
更新于2025-09-04 15:30:14
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Ionic conductive and dielectric properties of samarium isovalent doping in non-stoichiometric bismuth sodium titanate perovskite
摘要： Oxide ion-conducting solid electrolytes are of considerable importance as fuel cell component. Recently, Bi0.5Na0.5TiO3 (BNT)-based perovskite-structured oxides become a new hotspot of solid electrolyte since it has potential in oxygen ion conduction. Considerable ionic conductivity is achieved in a Bi deficient or an acceptor doping composition. In this work, the role of Sm content without lone pair electrons substituted for isovalent Bi is studied on the electrical properties of non-stoichiometric (Bi0.45Ca0.04)Na0.5TiO2.965 (BCNT). In the solid solution range, a transformation from resistive BCNT to dominated oxide ionic conductive process is revealed despite no additional designed vacancies involved. Interestingly, employment of smaller Sm cations by doping favors the plateau formation of dielectric permittivity at higher frequencies. Lone pairs substitution conception and shrinkage of lattice parameters are proposed to be responsible for the anomalous dielectric relaxation.
关键词： Bismuth sodium titanate,Lead free,Oxide ion conductors,Dielectrics
更新于2025-09-04 15:30:14
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Point defect chemistry of donor-doped bismuth titanate ceramic
摘要： This communication reports on the defect chemistry at room temperature of barium (Ba) doped bismuth titanate (Bi4Ti3O12), emphasizing the influence of the point defects on its electrical properties. Pure and Ba doped Bi4Ti3O12 were prepared by a conventional solid-phase reaction technique. The addition of Ba into the crystal structure of Bi4Ti3O12 was monitored by X-ray diffraction measurements combined with Rietveld refinement studies where it was determined that Ba occupies the bismuth (Bi) lattice sites as well as the presence of oxygen vacancies (V??O). The characterization of the point defects was carried out using impedance and electron spin resonance spectroscopies where the results support the models of compensation mechanisms dominated by electrical positive charges (h?) and oxygen vacancies (V??O).
关键词： defect chemistry,X-ray diffraction,Rietveld refinement,impedance spectroscopy,solid-phase reaction,barium doped bismuth titanate,electron spin resonance spectroscopy,electrical properties,oxygen vacancies
更新于2025-09-04 15:30:14